In the microelectronics industry as well as in other industries involving construction of microscopic structures (e.g. micromachines, magnetoresistive heads, etc.), there is a continued desire to reduce the size of structural features. In the microelectronics industry, the desire is to reduce the size of microelectronic devices and/or to provide greater amount of circuitry for a given chip size.
Effective lithographic techniques are essential to achieving reduction of feature sizes. Lithography impacts the manufacture of microscopic structures not only in terms of directly imaging patterns on the desired substrate, but also in terms of making masks typically used in such imaging. Typical lithographic processes involve formation of a patterned resist layer by patternwise exposing the radiation-sensitive resist to an imaging radiation. The image is subsequently developed by contacting the exposed resist layer with a material (typically an aqueous alkaline developer) to selectively remove portions of the resist layer to reveal the desired pattern. The pattern is subsequently transferred to an underlying material by etching the material in openings of the patterned resist layer. After the transfer is complete, the remaining resist layer is then removed.
For many lithographic imaging processes, the resolution of the resist image may be limited by anomalous effects associated with refractive index mismatch and undesired reflections of imaging radiation. To address these problems, antireflective coatings are often employed between the resist layer and the substrate (bottom antireflective coating or BARC) and/or between the resist and the atmosphere in the physical path along which the imaging radiation is transmitted (top antireflective coating or TARC). In the case of dry lithographic processes such as dry 193 nm lithography (not involving an immersion fluid in the radiation exposure step), the atmosphere would typically be air. In the case of immersion lithography, the atmosphere would typically be water.
The performance of an antireflective coating composition is largely dependent on its optical characteristics at the imaging radiation wavelength of interest. A general discussion regarding the generally desired optical characteristics of TARCs can be found in U.S. Pat. No. 6,274,295. Among the optical parameters of interest are the refractive index, the reflectance and the optical density of the TARC.
The antireflective coating composition must also have the desired physical and chemical performance characteristics in the context of its use in contact directly with or in close proximity to the resist layer and in the context of the overall lithographic process (irradiation, development, pattern transfer, etc.). Thus, the TARC should not excessively interfere with the overall lithographic process. It is highly desirable to have a TARC which can be removed during the image development step which typically involves dissolution of a portion of the resist in an aqueous alkaline developer solution.
The existing commercial TARC compositions do not possess the combination of optical properties and physical and chemical performance characteristics needed for high resolution 193 nm dry lithography. For example, some TARC compositions have a desired refractive index below 1.5, but are not soluble in aqueous alkaline developers, thus leading to extra complication and expense of a separate TARC removal step. Other TARC compositions have a desired refractive index, but adverse interaction with the resist leading to excessive film loss and loss of contrast in the resulting resist image or leading to formation of undesired T-top structures. Other TARC compositions have desired solubility in aqueous alkaline developer, but have too high a refractive index at 193 nm.
Thus, there is a need for TARC compositions suitable for use in dry 193 nm lithographic processes to enable high resolution lithography, especially in the context of imaging over topography on the underlying substrate.